Predictive model on wind-driven rainwater collections at curtain wall façades of tall buildings towards new vertical rainwater harvesting systems in tropical urban setting / Mozhgan Samzadeh

Mozhgan , Samzadeh (2024) Predictive model on wind-driven rainwater collections at curtain wall façades of tall buildings towards new vertical rainwater harvesting systems in tropical urban setting / Mozhgan Samzadeh. PhD thesis, Universiti Malaya.

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Abstract

Recent extreme precipitation events in frequency and intensity and increasing impervious surfaces – horizontally and vertically – in urban areas due to rapid horizontal and vertical expansion of built-up areas have resulted in increasing rainfall-runoff volume, amplifying urban flooding, as well as freshwater scarcity. Buildings can become more water-sustainable by adopting rainwater harvesting (RWH), which is a readily available alternative freshwater supply. However, the impact of vertical developments (a) on city level has resulted in distortion of the runoff process, 3D flow pattern, and sub-basin division, and (b) on building level has diminished the applicability of horizontal rooftop RWH because the ratio of roof surface area to vertical façade surface area has reduced significantly in tall buildings and roof RWH has been mainly replaced with roof garden concept. In light of these challenges, this research aims to evaluate the possibility of incorporating curtainwall building façades into an existing catchment area for Wind-Driven Rain (WDR) harvesting. This would divert WDR loads from the avenue runoff. This study employed (1) one-year in-situ measurement to quantify WDR amounts on building façades (rainfall-runoff) in urban areas and (2) semi-empirical models to predict the spatial distribution of WDR loads. In-situ measurements of WDR amount (Swdr) and meteorological parameters, i.e., wind direction (D), wind speed (U), and horizontal rainfall (Sh), were performed on a pilot building at the campus of Universiti Malaya in Kuala Lumpur, Malaysia. The influence of local wind speed (U) and horizontal rainfall intensity (Rh) on WDR intensity (Rwdr) was analysed. After the data cleaning process, only 65 out of 93 rain events were confirmed to be valid in-situ datasets for model validation. The Rwdr was subsequently calculated by the WDR equations of the semi-empirical models, i.e., ISO standard 15927-3 and ASHRAE standard 160P. The accuracy performance of both models to predict Rwdr were analysed mainly through analytical comparative assessments, i.e., coefficient of determinations (R²) and normalised root mean square deviation (NRMSD) between the in-situ dataset and the calculated dataset of Rwdr (mm/h). Through the cross-multiplication method using in-situ datasets and semi-empirical models’ datasets, the proposed WDR coefficients were determined for ISO (α) and ASHRAE (FL) models to predict the spatial distribution of WDR on tall building façades (up to > 50 m) in Kuala Lumpur. The results declared that the higher the building façade height, the greater the harvested Rwdr would be. The ISO model predicted 56% to 70% for non-potable usage reduction per square metre (lcd) at heights less than 10 metres to greater than 10 metres, respectively. The ASHRAE model predicted 57% to 109% for non-potable usage reduction per square metre (lcd) at heights less than 10 metres to greater than 50 metres, respectively. This research output, combined with further experimental investigations on actual tall building curtain walls, may lead to the adoption of vertical rainwater harvesting as a feasible method for water sustainability in tall buildings. The generated in-situ dataset can also be subjected to computational fluid dynamic analysis and model validation for WDR research in building science.

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